Computer display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a computer display screen or portion thereof with transitional graphical user interface, showing a first image according to the claimed design;

FIG. 2 is a front view of a second image thereof; and,

FIG. 3 is a front view of a third image thereof.

The process or period in which an image transitions to another image forms no part of the claimed design.

The longer-incremented broken-line showing of a computer and the shorter-incremented broken line showing of a display screen of the computer, as well as the features within the interface (including human figures), are included for the purpose of illustrating environmental structure and form no part of the claimed design. 

CLAIM The ornamental design for a computer display screen or portion thereof with transitional graphical user interface, as shown and described. 